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Equity Transactions - Additional Information (Detail) (USD $)
 9 Months Ended
Sep. 30, 2013
Sep. 30, 2012
May 31, 2013
Dec. 31, 2012
Equity, Class of Treasury Stock [Line Items]        
Common stock value $ 191,581,000      
Treasury stock, shares acquired 105,000 35,000    
Weighted average purchase price per share $ 187.61 $ 87.41    
Total cost of treasury shares acquired 19,700,000 3,100,000    
Treasury stock, shares 350,000     245,000
Treasury stock, at cost 37,438,000     17,734,000
Repurchased additional shares of common stock, shares     350,000  
Common stock remaining authorized for repurchase 350,000      
Repurchase program expiration date May 21, 2016      
Public Offering [Member]
        
Equity, Class of Treasury Stock [Line Items]        
Common stock, shares issued 1,300,000      
Common stock value $ 191,600,000